PHOTOSYNTHESIS AND GROWTH OF POPLAR TREES 265 



tions. These trees are outposts of a natural remnant forest of the Hortobagy- 

 PuBta near Ujszentmargita with a tree and bush vegetation of Quercus 

 rohur, Quercus cerris, Acer tataricurn, Fraxiniis excelsior, Pyrus communis and 

 Prunus spinosa. The investigations were carried out on sunny days in August 

 at maximum temperatures of more than 30°C and relative air humidities of 

 less than 40%. Besides the carbon dioxide assimilation, transpiration was 



25.7. 1957. 



Light intensity 



10- 



? 8 



O 

 U 



2- 



(b) 



1 T" 



5 10 



Light intensity ,1,000 Lux. 



Fig. 7. Assimilation in the minimum region of light: (a) daily march, (b) dependence 



on light. 



